The production and further processing of crystalline plates is increasingly required in the production of large flat screens, and in a large quantity.
Modern flat screens are increasingly replacing the old tube monitors, and are also becoming less and less expensive. These are based on TFT/LCD technology. In this context, LCD (Liquid Crystal Display) represents the use of liquid crystals in the individual pixels of the screen, and TFT stands for Thin Film Transistor. The TFTs are very small transistor elements which control the orientation, and therefore the light transmission, of the liquid crystals.
A flat-screen display consists of numerous pixels. In turn, each pixel consists of 3 LCD cells (subpixels), corresponding to the colors of red, green and blue. A 15-inch screen (measured diagonally) contains about 800,000 pixels or roughly 2.4 million LCD cells.
For understanding of the mode of operation:
A liquid crystal cell (LCD cell) works in a similar manner to polaroid sunglasses. If two polaroid glasses are held one above the other and then twisted with respect to each other, it is initially possible to see less and less and then nothing at all. This effect arises because polaroid glass is transparent only to light waves which vibrate in a specific plane. If two such glasses are held one above the other and twisted through 90° with respect to each other, some of the light can still pass through the first glass, but no longer through the second glass, since this is then transverse to the incoming light waves and filters them out.
An LCD cell works on the same principle. It consists of two polaroid glasses which are twisted through 90° with respect to each other and through which no light can therefore pass, in accordance with that explained above. A layer of liquid crystals, which has the natural property of turning the vibration plane of light, is located between these two polaroid glasses. This layer of liquid crystals is just thick enough that the light passing through the first polaroid glass is turned back through 90°, and can therefore also pass through the second polaroid glass, i.e. is visible to the viewer.
If the liquid crystal molecules are then turned away from their natural position by the application of an electrical voltage, less light passes through the cell and the corresponding pixel becomes dark. The corresponding voltage is produced by a TFT element which is part of every LCD cell. The light for the LCD display is produced in the rear part of the screen housing by small fluorescent tubes, as are used on a larger scale for illuminating rooms.
Since each pixel has three color filters for the colors of red, green and blue, the control of the transparency of these filters means that each pixel can assume a desired color mixture or a desired color.
For standard office applications, flat screens have outstanding sharpness and a sufficient color quality. In ergonomic terms, TFTs also have much to offer: smaller space requirement, a power consumption which is only a third of that of a tube monitor and significantly lower emission of radiation.
As is conventional in microelectronics, the production of TFT screens requires so-called ultra-clean rooms. This is necessary because, in view of the small size of the line-carrying structures, even small particles can cause line interruptions during the production process. In the production of a TFT screen, such a line interruption would result in the failure of a pixel.
A clean room is a room in which the concentration of airborne particles is controlled. It is constructed and used in such a manner that the number of particles introduced into the room or produced and deposited in the room is as small as possible, and other parameters, such as temperature, humidity or air pressure, are controlled as required.
On the one hand, TFT screens are currently becoming less and less expensive, and on the other hand the demand for screens with enormous proportions is increasingly standing out, all the more so because screens of this type firstly can be used very easily at major events and secondly are available in affordable price ranges due to modern production technology.
However, the production of large screens requires the use of special machines even in ultra-clean rooms to handle the large-surface-area, thin glass plates required in this case.
For this purpose, it is possible to use primarily multi-axle industrial robots.
The use of a wide variety of embodiments of multi-axle industrial robots in technology for producing a wide variety of products can be gathered from the prior art. Industrial robots of this type are used in large halls mostly for transporting unmanageable and heavy loads, but can also be used beneficially in the production of smaller machine parts. What matters in all cases is the reproducible precision of the movement sequences of the individual grasping operations, transport movements and setting-down operations.
Here, the conditions in which these movement sequences take place are mostly unimportant. For example, it is mostly immaterial which noise emission such a movement sequence causes, or whether such an operation is associated with the movement of dust or a more or less large escape of lubricant. Unavoidable abrasion of moving machine parts which cause friction is also mostly unremarkable.
By contrast, natural ramifications of this type must be taken into consideration when working in an environment at risk from contamination, for example in the food-processing industry or in the pharmaceutical industry.
Thus, EP 1 541 296 A1 discloses a manipulator, such as an industrial robot, for use in an environment at risk from contamination, having a number of scavenging chambers, which can be charged with a scavenging medium, in the region of drive units of the manipulator. The object to be achieved in the case of such a device is to further develop the device to such an extent that the manipulator can safely be used in an environment at risk from contamination in a structurally simple manner and therefore, in particular, at low cost.
This object is achieved by a dedicated scavenging chamber being associated with each of a plurality of groups of drive units (claim 1).
Although the environment in which such an industrial robot is to be used is more sensitive to contamination and therefore also places higher demands on the design configuration compared to a normal environment, special demands of this type cannot be compared with the conditions demanded in ultra-clean rooms.
Apart from what has been mentioned above, large, thin glass plates such as those used for producing large TFT screens are extremely sensitive to very small shocks owing to their crystalline structure and concurrent relatively large mass. Therefore, an industrial robot is also unsuitable for handling large, thin glass plates in ultra-clean rooms because it lacks sensitivity and positional accuracy.
DE 10 2005 062 936 A1 discloses an apparatus and a process for the positional correction of disk-shaped elements transported by means of a conveying element.
This positional correction should take place automatically. In order to achieve this object, the intention is substantially to protect the fact that it is possible to determine detection instants at which an outer contour of the disk-shaped element passes in each case into a detection region of a sensor. The handling of large, thin glass plates in ultra-clean rooms is not possible using this apparatus.
DE 692 07 737 T2 discloses an apparatus for handling and orienting bundled, flat articles, in particular consisting of cardboard or corrugated paper plates or blanks. The object on which this apparatus is based is that it should be designed at lower cost and in a more spatially compact manner compared with the prior art. This object is substantially achieved in that two conveying elements which are displaceable vertically in relation to each other can be displaced laterally, and that the other conveying element comprises a series of driven rollers which are separate from each other and between which there are driven balls. This apparatus is intended to handle bundled, flat articles of cardboard or corrugated board. The handling of glass plates is not possible with this apparatus.
DE 33 11 116 A1 relates to a process and an apparatus for orienting plates on a roller table by means of forces acting on the plates. The process in question is characterized in that forces of different direction and magnitude are transmitted, via roller contact, to a plurality of regions of a moving plate. A suggestion to handle large, thin glass plates in ultra-clean rooms cannot be gathered from this process or this apparatus.